One form of signal transduction involves a number of proteins that regulate cyclic nucleotide levels in cells in response to the interaction of cell-surface receptors with specific ligands. These transducing proteins (G proteins) mediate the effects of hormones, neurotransmitters and sensory stimuli. In order to understand the function, distribution and structure of these proteins, we will isolate the DNA that encodes them. The DNA will be used to probe the structure of the gene family that encodes G proteins and the nature of the tissue-specific expression of these genes. We will start by isolating cDNA clones that correspond to the Alpha, Beta and Gamma subunits of visual transducin. We will characterize these cDNAs and use them to isolate tissue-specific cDNA clones and genomic clones that cross hybridize with transducin. We will characterize this gene family with respect to the tissues in which different genes get expressed and the mechanisms involved in specific gene expression. We will use the probes to examine variants that are defective in G protein function. We will develop an expression system to allow the cloned genes to be expressed in variant cell lines. Finally, we will introduce specific nucleotide changes in the cloned DNA and study the behavior of the modified gene products.